1. Field of the Invention
The present invention relates to a liquid crystal display in which a tape carrier having an IC mounted thereon is arranged on an edge portion of a liquid crystal panel, and a lead wire on the tape carrier is connected to an electrode terminal on the liquid crystal panel.
2. Description of the Related Art
In general, a dot matrix type of liquid crystal display has a structure such that a plurality of electrode patterns extending in two directions perpendicular to each other are formed on opposed surfaces of an upper glass substrate and a lower glass substrate of a liquid crystal panel, and a plurality of electrode terminals extending from the electrode patterns (a common electrode and many segment electrode patterns) extending in the row direction or the column direction are formed on an edge portion of each glass substrate. Further, a plurality of tape carriers (also called tape carrier packages) are suitably arranged on the edge portion of each glass substrate. Each tape carrier includes a flexible substrate, an IC chip mounted on the flexible substrate, and a plurality of lead wires formed on the flexible substrate. The lead wires at one end portion of each tape carrier are connected through anisotropic conductive adhesive or the like to the electrode terminals on the corresponding glass substrate. The lead wires at the other end portion of each tape carrier are connected to a control circuit such as a printed wiring board. Thus, the liquid crystal panel is driven by the IC chip.
In the case where 480 electrode terminals are formed on the edge portion of the liquid crystal panel along one end line thereof and 100 output terminals are formed on each tape carrier, for example, a conventional arrangement is such that five tape carriers each having this structure are juxtaposed at equal intervals on the edge portion of the liquid crystal panel to connect the lead wires and the electrode terminals. In this case, the total number of the output terminals that can be used on all the tape carriers is greater than the total number of the electrode terminals to be connected. Accordingly, a few unused lead wires not connected to the electrode terminals are present on a part of the tape carriers, and these unused lead wires may be considered as dummy patterns.
In such a liquid crystal display wherein a plurality of tape carriers each having a plurality of lead wires are juxtaposed on an edge portion of a liquid crystal panel having a plurality of electrode terminals to connect the lead wires of each carrier tape to the electrode terminals of the liquid crystal panel, a pitch of the lead wires must be made smaller than a pitch of the electrode terminals. Accordingly, the electrode terminals are wired in a manner as shown in FIG. 3. That is, a plurality of electrode terminals 2 of a liquid crystal panel 1 are wired so as to converge toward a corresponding tape carrier 4 having a plurality of lead wires 5 to be connected to these electrode terminals 2. When a plurality of tape carriers 4 are juxtaposed at equal intervals on the edge portion of the liquid crystal panel 1 as mentioned above, two of the electrode terminals 2 which are adjacent to each other but connected to two adjacent ones of the tape carriers 4 (i.e., two electrode terminals 2a and 2b or 2c and 2d in FIG. 3) cannot be set in line symmetry. Thus, the two adjacent electrode terminals 2 are unavoidably unbalanced in a wiring form in such a manner that the electrode terminal 2a becomes considerably longer than the electrode terminal 2b, for example. Such a large difference in length between the two adjacent terminals 2 causes a large difference in wiring resistance therebetween. As a result, there occurs nonuniformity of display contrast between adjacent pixels formed by adjacent electrode patterns 3 extended to the two adjacent electrode terminals 2.
Further, in the case where unused lead wires not connected to the electrode terminals 2 are present on the tape carriers 4 arranged on the edge portion of the liquid crystal panel 1, a portion of a certain one of the tape carriers 4 for forming the unused lead wires is formed as a lead pitch increased area 7 in which a pitch of the unused lead wires is locally increased over a pitch of the lead wires 5 connected to the electrode terminals 2. Conventionally, no attention is paid to a difference in length between two adjacent electrode terminals 2m and 2n respectively connected to two lead wires 5a and 5b adjacent to each other with the lead pitch increased area 7 interposed therebetween. Accordingly, the electrode terminal 2m becomes considerably longer than the electrode terminal 2n as shown in FIG. 3, causing a large difference in wiring resistance between the two adjacent electrode terminals 2m and 2n. As a result, there is a possibility that nonuniformity of display contrast may occur between adjacent pixels formed by adjacent electrode patterns 3 extended to the two adjacent electrode terminals 2m and 2n.
In FIG. 3, reference numeral 6 denotes an IC chip mounted on each tape carrier 4 to drive the liquid crystal panel 1. The IC chip 6 is connected to the lead wires 5 formed on the corresponding tape carrier 4.